Portugal is still the country with the highest TB incidence rate in Western Europe1–3; although a recent decrease in TB incidence rate has placed the country close to the low incidence goal.2 Despite a national TB incidence rate of 21.1/100000 inhabitants in 2013, Penafiel municipality registers the highest TB incidence rate in the whole country (83.4/100000 inhabitants in 2013).2 Penafiel municipality is part of Northern Portugal region (NUTS II) and it is located in a geographic area designated as Vale de Sousa. The large majority of its 28 parishes are quite industrialized, although in some of them the primary sector still represents an important part of the economy. The mining sector, particularly exploration of granite quarries, is an important economic sector in Penafiel and other neighbouring counties in the geographic region of Vale de Sousa.4 Therefore, the large exposure of Penafiel's mining sector workforce to prolonged inhalation of crystalline silica has been pointed out has one of the major factors for TB high incidence rate in this region.5

In order to identify longitudinal trends of TB incidence rate in Penafiel and Northern Portugal and to describe the behaviour of silica-related diseases and other social and health-related indicators in the region, we performed a longitudinal study that included every active new TB case notified in Penafiel and Northern Portugal between January 1st, 2002 and December 31st, 2012. The data source was the Portuguese Tuberculosis Surveillance System (SVIG-TB) and the information was up-to-date until December 31st, 2012. The SVIG-TB is the notification and follow-up system of the TB cases in Portugal, supervised by the Directorate-General of Health (DGS).6

For all predictors, data were collected yearly and obtained from the following national institutions: Statistics Portugal (INE), Employment and Vocational Training Institute (IEFP), Directorate General of Prison Services (DGSP), Institute on Drugs and Drug Addiction (IDT), Institute of Social Security (ISS), Directorate General of Energy and Geology (DGEG) and National Health Institute Doutor Ricardo Jorge (INSA).

TB incidence rate and other incidence rates are expressed as the rate per 100000 inhabitants. A time-trend descriptive analysis was carried out to substantiate the dynamics of the TB incidence and other collected data in both regions over the study period.

During the period studied, a total of 675 new TB cases were notified in Penafiel, with an average decrease of the TB incidence rate of 1.41% per year (from 95.5/100000 inhabitants in 2002 to 82.1/100000 inhabitants in 2012). In the same period, a total of 16364 new cases were notified in Northern Portugal, with a similar average decrease of 1.19% per year (from 35.8/100000 inhabitants in 2002 to 24.4/100000 inhabitants in 2012).

As expected, a declining time-trend for the TB incidence rate was exhibited by both regions during the studied period. Socio-demographic and health-related indicators of both regions are presented in Table 1.

Table 1.

Relevant socio-demographic and health-related indicators of Penafiel and Northern Portugal.

Years

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

Population density (per km2)

Northern Portugal

187.8

188.1

188.2

191.4

191.5

191.6

191.2

190.9

190.3

190.0

189.0

Penafiel

340.3

341.2

342.2

342.7

343.0

343.1

342.5

341.7

340.8

340.3

338.5

Elderly dependency ratio (%)

Northern Portugal

21.5

21.8

22.2

22.5

22.8

23.1

23.5

24.0

24.8

25.3

25.9

Penafiel

15.9

16.1

16.4

16.6

16.6

16.6

16.8

17.2

17.8

18.2

18.5

Unemployment rate (%)

Northern Portugal

4.0

5.0

5.4

5.7

5.4

4.6

4.9

6.0

6.2

6.7

7.8

Penafiel

2.8

3.8

4.1

3.9

3.5

3.2

3.7

5.2

5.3

6.4

8.0

Immigration rate (%)

Northern Portugal

n/a

n/a

n/a

n/a

n/a

n/a

1.31

1.38

1.39

1.44

1.38

Penafiel

n/a

n/a

n/a

n/a

n/a

n/a

0.55

0.56

0.54

0.47

0.42

Medical doctors (per 100000)

Northern Portugal

281.6

288.5

296.6

306.8

315.4

324.5

335.0

347.1

362.3

376.0

385.2

Penafiel

84.5

87.0

85.4

89.4

92.0

96.1

100.4

113.1

130.0

142.6

142.0

Mining sector work force (per 100000)

Northern Portugal

75.7

73.7

75.1

71.0

79.2

71.0

59.8

56.1

59.8

61.1

56.7

Penafiel

886.1

748.4

797.1

732.8

236.3

410.6

517.3

547.4

634.6

630.0

483.0

Silicosis notification rate (per 100000)

Northern Portugal

4.3

4.3

6.6

3.7

2.1

2.7

2.6

3.1

2.1

2.4

2.4

Penafiel

54.0

69.0

125.3

83.9

50.8

107.1

78.4

80.0

89.9

112.1

84.9

Silicosis prevalence rate (per 100000)

Northern Portugal

78.5

78.2

80.0

88.0

85.3

82.3

79.6

76.5

73.9

70.9

67.9

Penafiel

560.8

588.2

645.7

730.1

739.1

788.3

803.5

834.3

875.2

901.3

959.0

Silicotubercolsis (% of total TB cases)

Northern Portugal

0.8

0.4

0.2

0.4

0.6

0.7

0.7

0.7

0.6

1.9

0.8

Penafiel

0.0

1.5

0.0

0.0

4.5

4.2

7.6

12.1

3.6

10.0

8.5

HIV notification rate (per 100000)

Northern Portugal

15.9

15.1

14.9

13.9

13.0

12.4

12.3

10.3

9.3

7.4

7.4

Penafiel

8.3

8.3

11.0

11.0

11.0

11.0

8.3

8.3

6.9

15.2

12.5

HIV/TB co-infection (% of total TB cases)

Northern Portugal

13.3

14.6

13.1

12.9

11.7

11.5

10.8

10.9

7.6

7.8

7.7

Penafiel

4.3

4.5

6.2

5.8

3.0

6.3

1.5

1.7

1.8

1.4

0.0

Addiction related TB (% of total TB cases)

Northern Portugal

28.1

23.4

22.3

24.6

24.8

24.6

20.4

20.8

19.8

18.2

17.7

Penafiel

13.0

14.9

13.8

11.5

15.2

12.5

7.6

6.9

9.1

15.7

20.3

Immigration related TB (% of total TB cases)

Northern Portugal

2.7

2.6

2.4

3.5

2.7

3.3

3.4

4.1

4.2

4.5

4.3

Penafiel

0.0

0.0

0.0

0.0

0.0

2.1

0.0

1.7

0.0

0.0

1.7

Homeless related TB (% of total TB cases)

Northern Portugal

2.8

3.6

3.8

4.5

4.4

3.8

2.7

2.8

3.2

3.3

3.0

Penafiel

1.4

1.5

1.5

1.9

1.5

0.0

0.0

0.0

0.0

1.4

1.7

Incarceration related TB (% of total TB cases)

Northern Portugal

1.1

0.4

0.7

1.2

0.9

0.9

0.9

0.9

1.0

0.9

1.5

Penafiel

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

From a socio-demographic point of view and in comparison with Northern Portugal, Penafiel municipality presents a higher population density, a lower elderly dependency ratio and a much lower number of medical doctors. As previously mentioned, mining industry is a strong economic sector in Penafiel; therefore the proportion of mining workers in the population is frankly above the rest of the Northern Portugal region, with a subsequent significantly higher silicosis notification and prevalence rates in Penafiel, with the latter presenting an increasing trend during our study period. The same increasing trend was reported for new cases of silicotuberculosis in Penafiel, while over the same period Northern Portugal values remained stable.

As for the other TB related risk factors, although HIV notification rates are similar between both regions, Penafiel reports a lower HIV/TB co-infection rate, as well as lower notification rates for all other TB related risk factors collected (immigration, incarceration, addiction and homeless).

Other collected social and health-related indicators, like higher population density and lower number of medical doctors, might also play an important role in Penafiel's higher TB incidence.

Author contributions

Raquel Duarte and A. Rita Gaio conceived the project idea. Daniel Coutinho and Pedro Sousa collected the data. Olena Oliveira and A. Rita Gaio conducted the analyses. All authors interpreted and discussed the results. All authors wrote the manuscript. All authors have read and approved the final version.